The clutch actuator for manual transmission motor vehicles comprises a selectively displaceable element which is connected to the release member of the clutch assembly to separate two rotatable elements of the clutch, which elements are normally frictionally coupled to transfer energy from the engine crank shaft to the transmission input shaft. In the case of a hydraulic actuator, the actuator comprises the slave portion of a hydraulic master cylinder/slave cylinder assembly wherein the master cylinder is mounted so as to be directly operated by the clutch pedal.
As is well known, the release element of the clutch rotates at engine speed when the clutch is engaged and slows down and may eventually stop when the clutch is released or disengaged to permit a gear change. The actuator, on the other hand, is nonrotating. That is, the body of the actuator must be secured against rotation to a structural component such as the transmission housing of the clutch housing. Therefore, the clutch actuator must be connected to the release member through a bearing, commonly called a throw-out or release bearing.
The actuator can be an external slave unit mounted off axis relative to the transmission input shaft or it can be a concentric slave cylinder mounted concentrically with respect to the transmission input shaft. The off axis arrangement involves a lever arm connected between the actuator output element and the clutch release member. The typical concentric arrangement requires no such lever arm. Instead, the cylinder body of the actuator is fixed to the clutch bell housing or to the face of the transmission housing and the axially translatable piston is connected to the outer race of the throw-out bearing. The inner race is in turn connected to the clutch release element.
Examples of concentric clutch actuators are shown for example in U.S. Pat. Nos. 4,585,106 or 4,585,107; 4,585,108; 4,585,109; 4,609,087; 4,264,290; 4,660,694; 4,684,003; 4,687,084 and 4,708,228, all assigned to the assignee of the present application.
Whereas the concentric slave cylinders disclosed in the above-identified U.S. patents are generally satisfactory, there are certain structural aspects of the prior art concentric slave cylinders that render them susceptible to structural failure.